To analyze characteristics of a substance, a measurement method has hitherto been used which includes the steps of holding a specimen on an aperture array structure (i.e., a flat-plate periodic structure that is made up of plural unit structures each having an aperture), applying an electromagnetic wave to the aperture array structure on which the specimen is held, and analyzing a transmission spectrum of the electromagnetic wave, thereby detecting characteristics of the specimen. One practical example is a method of applying a terahertz wave to a specimen, such as a protein attached to a metal mesh filter, for example, and analyzing a transmission spectrum of the terahertz wave.
As an example of that type of related-art method of analyzing a transmission spectrum using an electromagnetic wave, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2008-185552) discloses a measurement method of applying an electromagnetic wave to an aperture array structure having an aperture region (specifically, a mesh-like conductive plate), on which a specimen is held, from a direction oblique to a direction perpendicular to a principal surface of the aperture array structure, measuring the electromagnetic wave having transmitted through the aperture array structure, and detecting characteristics of the specimen based on a phenomenon that a position of a dip waveform, which appears in the frequency characteristic of a measured value, is shifted depending on the presence of the specimen.